I. Field of the Invention
This invention relates to cold forming tools and more particularly to tools, apparatus and methods used in the rolling and tooth forming of cylindrical elements.
II. Description of the Prior Art
Finishing of cylindrical metal parts to a desired smoothness or quality of finish can be accomplished by many different types of machining operations and machines, e.g. turning or honing machines, grinders, sanders, EDM and ECM machines. The smoothness obtained is determined by the speed, feed and depth of cut of the particular machine which is performing the task. Generally, a straight turned part is ground after the turning operation if a very smooth finish is desired, i.e. finishes in the 5-25 micro-inch range. Sanding, polishing or buffing machines can also produce similar finishes but these usually lie in the 15 to 25 micro-inch range.
The cold working of cylindrically shaped parts to achieve a desired shape or size is old in the art and has been carried out with a variety of machines and methods and the final surface finish of a part rolled or ironed would have some degree of smoothness upon completion of the particular process.
The very early prior art of rolling metals dates back to the late 1800's. Methods for rolling metals, for example, are seen in a patent to Loughrin, No. 625,575, where an apparatus is shown for rolling a square bar into a cylindrical shape. However, the objective of the forming process was to roll the part to a particular form or shape rather than to a particular shape, finish and size. Later processes for rolling spindles and the like are shown in a U.S. Pat. No. 1,504,024 to Clark. The purpose of this particular invention was to straighten spindles, rods, shafts and similar articles. Again, the particular surface finish and size were not the main objectives in that particular patent but burnishing of the surface as part of the process did occur. There are many patents in the field for rolling metals which include the manufacture of rivets, rivet pins, dowels, roller bearings, small cylindrical parts and the like. These are shown in U.S. Pat. Nos. 1,446,447, 2,825,251 and 3,044,332.
The roll sizing process of a surface displaces rather than removes the minute surface irregularities produced with cutting tools and may be applied to both internal and external surfaces. The U.S. Pat. No. 2,480,043 to Paulus et al shows a method for journaling a shaft and bushing which uses tools to iron the bushing onto the shaft. The tight fit of the bushing on the shaft is disrupted by a rolling operation between a pair of opposing die members. The radially applied pressure causes the bushing material to flow and increases its circumferential length on the shaft. Still another more recent U.S. Pat. No. 4,208,773 to Killop shows an apparatus for burnishing gear teeth by use of opposed die racks. Here, the tooth form of the gear is altered by axially crowning the surface of the tooth form by burnishing.
The inventor in the instant patent set out to roll cylindrical components thereby generating plain bearing surfaces and to provide the required pre-roll diameter size on cylindrical components for spline and serration cold forming operations. The major problem in rolling teeth on such a surface is that the diameter of the surface to be rolled is extremely critical and must be held to close tolerances. The rolling diameter of the workpiece is selected so that the material volume which is to be displaced from the diameter below the surface will be forced into a tooth form above the initial diameter of the workpiece. Therefore, the initial diameter of the part to be rolled is aproximately the pitch diameter of the tooth to be formed. In the normal processes for manufacturing an axle or a shaft which is going to have a spline or gear tooth form rolled on it, the stages of production preceding the rolling of the tooth form are very critical. The piece part is usually first machined on a turning machine, such as a lathe, to a predetermined diameter and then it is ground to hold the diameter within a specific range of tolerances so that when a tooth form is rolled on the shaft, it will have the correct pitch diameter, tooth form, addendum and dedendum.
An object of this invention is to eliminate some of the steps used in the normal production process for the manufacture of the shaft prior to the rolling operation for making the gear tooth form. Another object of the invention is to utilize only a rough finishing operation such as turning on the diameter prior to the rolling operation of the instant invention. Another object of the invention is to displace metal on the surface of the shaft to be rolled in such a way that the final diameter will be within the tolerance range for forming a proper tooth form of the desired pitch diameter.
An object of the invention is to finish shafts to a final finish that preferably does not exceed 25 micro-inches. A further object of the invention is to eliminate the need for a pre-grind or finish-grind of the shaft diameter prior to the tooth rolling operation. An object of the invention is to roll size cylindrical surfaces and reduce the diameter of the surface by cold working the surface to the correct size. Still another object of the invention is to provide a tool which will provide the appropriate finish and desired improvement of the workpiece surface and at the same time reduce the cost of manufacture.
Another object of this invention is to incorporate a roll sizing tool and a tooth forming tool onto the same machine so that the piece part can be pre-sized by the roll sizing tool and subsequently rolled by the tooth forming tool to form the desired spline, serration, thread or gear tooth form. The tools disclosed herein can be used on such machines as shown in U.S. Pat. No. 2,995,964 to Drader, U.S. Pat. No. 3,818,736 to Blue and U.S. Pat. No. 3,982,415 to Killop.